Re: [PATCH net-next V2 1/3] tap: use build_skb() for small packet

[Jason Wang]

On 2017年08月16日 18:24, Eric Dumazet wrote:

On Wed, 2017-08-16 at 11:55 +0800, Jason Wang wrote:

On 2017年08月16日 11:45, Eric Dumazet wrote:

You do realize that tun_build_skb() is not thread safe ?

Ok, I think the issue if skb_page_frag_refill(), need a spinlock
probably. Will prepare a patch.

But since tun is used from process context, why don't you use the
per-thread generator (no lock involved)

Haven't noticed this before.

tcp_sendmsg() uses this for GFP_KERNEL allocations.

Untested patch :

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 
5892284eb8d05b0678d820bad3d0d2c61a879aeb..c38cd840cc0b7fecf182b23976e36f709cacca1f
 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -175,7 +175,6 @@ struct tun_file {
        struct list_head next;
        struct tun_struct *detached;
        struct skb_array tx_array;
-       struct page_frag alloc_frag;
  };

struct tun_flow_entry {

@@ -578,8 +577,6 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
                }
                if (tun)
                        skb_array_cleanup(&tfile->tx_array);
-               if (tfile->alloc_frag.page)
-                       put_page(tfile->alloc_frag.page);
                sock_put(&tfile->sk);
        }
  }
@@ -1272,7 +1269,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
*tun,
                                     struct virtio_net_hdr *hdr,
                                     int len, int *generic_xdp)
  {
-       struct page_frag *alloc_frag = &tfile->alloc_frag;
+       struct page_frag *alloc_frag = &current->task_frag;
        struct sk_buff *skb;
        struct bpf_prog *xdp_prog;
        int buflen = SKB_DATA_ALIGN(len + TUN_RX_PAD) +
@@ -2580,8 +2577,6 @@ static int tun_chr_open(struct inode *inode, struct file 
* file)
        tfile->sk.sk_write_space = tun_sock_write_space;
        tfile->sk.sk_sndbuf = INT_MAX;

- tfile->alloc_frag.page = NULL;

-
        file->private_data = tfile;
        INIT_LIST_HEAD(&tfile->next);

Tested-by: Jason Wang <jasow...@redhat.com>
Acked-by: Jason Wang <jasow...@redhat.com>